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Measuring the pressure angle of gears

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Michael Cox 107/09/2010 13:31:34
555 forum posts
27 photos
Does anyone have any ideas about measuring the pressure angle of gears?
I have tried measuring the curvature of gear teeth form photos taken with a camera and with a USB microscope and then using Ivan law's circular approximation to estimate the pressure angle. However, I am getting very inconsistent results. Any other ideas?
Mike
Joseph Ramon07/09/2010 14:31:49
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107 forum posts
Flatten out a blob of blu-tac or plasticine on the bench.
 
Roll the gear over the top to leave the impression of a rack. 
 
In principle it should leave a straight-sided impression the angle of the sides being the pressure angle.
 
In practice it won't be perfect, especially if the gears are small, but it should distinguish different angles.
 
Joey 
JasonB07/09/2010 16:27:06
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25215 forum posts
3105 photos
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Download the file Gearpa.zip from tthis page and you should be able to measure your gears, Marv's got a lot of useful little programmes there.
 
Jason
Gordon W08/09/2010 09:36:20
2011 forum posts
Last time I did this was about 30 yrs ago, and a big gear, 2 ft. dia and 13 teeth, but might help. Trace tooth on paper and measure angle. From the physical dims of the gear, and assuming yours is a standard pressure angle, with the help of the tables, should be able to be fairly sure. Not well explaiined but might help.
Michael Cox 108/09/2010 11:10:34
555 forum posts
27 photos
Thanks for all the ideas.
I had tried some of these ideas.
The plasticine method sounds easy in principle but the gear I have been trying to measure is a MOD 1 plastic 30 tooth change gear for a minilathe. This is small and the plasticine tends to stick between the teeth.
The Gearpa.zip method also gave difficulties because differences were two small to measure reliably.
Gordons idea would certainly work on a large gear but is more difficult for small gears.
I have now convinced myself that the gear has a pressure angle of 20 degrees using the method described here:
Mike
Stub Mandrel08/09/2010 21:03:24
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4318 forum posts
291 photos
1 articles
The minilathe change gears are20 degrees. pm me your email and I'll send you some stuff about how to cut your own mini lathe gears with minimal equipment. Also see my photo album.
 
Neil
 

Robert Miller 108/09/2010 21:14:17
19 forum posts
There is a description of how to do this in Huston Tx's home metal shop club's latest newsletter at:
 
http://www.homemetalshopclub.org/news/10/newsletter1008.pdf#Page=8&view=fitH

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